"Sub-Subevent" System HealthBar.Pin.PinnedUID = EnemyFamily.UID (HealthBar.destroy)
I'd guess this line doesn't actually do any picking, so no health bars are picked here. You could try:
a) saving health bar UID into EnemyFamily variable and using pick by UID condition when destroying the health bar
b) if there is no overlapping in your enemies, pick closest health bar to the dying enemy and destroy that
c) something more elegant :)